U.S. patent number 4,321,968 [Application Number 06/152,227] was granted by the patent office on 1982-03-30 for methods of using aqueous gels.
This patent grant is currently assigned to Phillips Petroleum Company. Invention is credited to Elmer E. Clear.
United States Patent |
4,321,968 |
Clear |
March 30, 1982 |
Methods of using aqueous gels
Abstract
Carboxymethylhydroxyethyl cellulose in aqueous brine solutions
is gelled by the addition of an alkaline earth metal hydroxide such
as calcium hydroxide. The gelled compositions have utility as water
diversion agents, pusher fluids, fracturing fluids, drilling muds,
work-over fluids, and completion fluids.
Inventors: |
Clear; Elmer E. (Bartlesville,
OK) |
Assignee: |
Phillips Petroleum Company
(Bartlesville, OK)
|
Family
ID: |
22542033 |
Appl.
No.: |
06/152,227 |
Filed: |
May 22, 1980 |
Current U.S.
Class: |
166/275;
166/308.2; 166/300; 507/113; 507/215; 166/293; 166/302; 175/65;
507/922; 507/933; 507/936 |
Current CPC
Class: |
C09K
8/588 (20130101); C09K 8/514 (20130101); C09K
8/10 (20130101); C09K 8/90 (20130101); C09K
8/68 (20130101); Y10S 507/936 (20130101); Y10S
507/933 (20130101); Y10S 507/922 (20130101) |
Current International
Class: |
C09K
8/58 (20060101); C09K 8/588 (20060101); C09K
8/62 (20060101); C09K 8/02 (20060101); C09K
8/50 (20060101); C09K 8/514 (20060101); C09K
8/10 (20060101); C09K 8/60 (20060101); E21B
043/22 (); E21B 043/267 (); E21B 033/138 () |
Field of
Search: |
;166/270,271,273,274,275,280,281,293,300,35R,308 ;175/65
;252/8.55R,8.55D,8.5A,8.5C |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
7507124 |
|
Feb 1976 |
|
NL |
|
1528258 |
|
Oct 1978 |
|
GB |
|
Primary Examiner: Novosad; Stephen J.
Assistant Examiner: Suchfield; George A.
Claims
I claim:
1. In a method wherein a fluid medium is introduced into a borehole
in the earth and into contact with the pores of a subterranean
formation penetrated by said borehole, the improvement wherein at
least a portion of said fluid medium comprises a gelled aqueous
brine solution having at least 1,000 ppm divalent cations
containing an effective water thickening amount of CMHEC
characterized by a degree of substitution (DS) ranging from about
0.1 to about 1 and a molar substitution (MS) ranging from about 1
to about 4 and an effective gelling amount of an alkaline earth
metal hydroxide.
2. A method according to claim 1 wherein
said borehole comprises an injection well,
said formation comprises an oil-bearing formation and is also
penetrated by a production well,
said method is a fluid drive process carried out for the recovery
of oil from said formation by injecting a drive fluid into said
formation via said injection well and driving oil to said
production well, and
said fluid medium comprising said aqueous gel is introduced into
said injection well and into the pores of said formation.
3. A method according to claim 2 wherein said fluid drive functions
as a mobility buffer and follows injection of a surfactant
slug.
4. A method according to claim 1 wherein said method comprises a
method for drilling a borehole into the earth
a drill bit is actuated in said borehole in said contact with said
formation and penetrates same in the presence of said fluid medium,
and
said fluid medium, together with formation solids entrained
therein, is removed from said borehole.
5. A method of fracturing in a well traversing a formation which
comprises injecting into the well a fracturing fluid wherein at
least a portion of said fracturing fluid passing through the pores
of said formation comprises a gelled aqueous brine solution having
at least 1,000 ppm divalent cations containing an effective water
thickening amount of CMHEC characterized by a degree of
substitution (DS) ranging from about 0.1 to about 1 and a molar
substitution (MS) ranging from about 1 to about 4 and an effective
gelling amount of an alkaline earth metal hydroxide.
6. A method according to claim 5 wherein the fluid contains a
granular material (propping agent).
7. The method of treating a well traversing a producing formation
which comprises injecting a fracturing fluid into the pores of said
formation wherein at least a portion thereof comprises a gelled
aqueous brine solution having at least 1,000 ppm divalent cations
containing an effective water thickening amount of CMHEC
characterized by a degree of substitution (DS) ranging from about
0.1 to about 1 and a molar substitution (MS) ranging from about 1
to about 4 and an effective gelling amount of an alkaline earth
metal hydroxide into a confined zone of said well at a rate
sufficient to increase the pressure exerted in said zone until
formation fracture occurs, continuing to inject said fluid into the
formation, thereafter permitting the gel to break and producing the
well.
8. A method according to claim 7 wherein the fluid contains a
granular material (propping agent).
Description
This invention relates to new aqueous gels and uses thereof. In
accordance with another aspect, this invention relates to gelled
aqueous brines containing carboxymethylhydroxyethyl cellulose
(CMHEC) and a gelling agent. In a further aspect, this invention
relates to a method of gelling brines comprising the addition of
carboxymethylhydroxyethyl cellulose (CMHEC) and a gelling agent. In
accordance with a further aspect, this invention relates to the use
of the instant compositions as water diversion agents, pusher
fluids, fracturing fluids, drilling muds, and work-over or
completion fluids.
Accordingly, an object of this invention is to provide novel
thickened and gelled fluids.
A further object of this invention is to provide thickened and
gelled fluids useful in the treatment of wells.
Other aspects, objects, and the several advantages of this
invention will become apparent to those skilled in the art upon
reading this disclosure and the appended claims.
In accordance with the invention, a gelled aqueous composition is
provided which comprises an aqueous brine solution containing
carboxymethylhydroxyethyl cellulose (CMHEC) and a sufficient amount
of alkaline earth metal hydroxide to cause gelation and form a
gelled composition.
In accordance with one embodiment of the invention, brine solutions
are gelled with carboxymethylhydroxyethyl cellulose (CMHEC) and an
alkaline earth metal hydroxide, such as calcium hydroxide.
The aqueous gels of the invention are particularly useful in
operations wherein a fluid medium is introduced into a bore hole in
the earth as in secondary recovery operations, well treating
operations, well completion operations, etc.
Carboxymethylhydroxyethyl cellulose (CMHEC) polymers suitable for
use in the instant process are characterized by a degree of
substitution (D.S.) in the broad range of about 0.1 to about 1,
preferably about 0.2 to about 0.5 and a molar substitution (M.S.)
in the broad range of about 1 to about 4, preferably about 2 to
about 3. The "degree of substitution" designates the average number
of hydroxyl groups per cellulosic anhydroglucose unit which are
substituted with carboxymethyl groups. The "molar substitution"
designates the average number of moles of hydroxyethyl groups
present per cellulosic anhydroglucose unit. A commercially
available polymer suitable for use in the invention is CMHEC of 0.4
carboxymethyl D.S. and 2.0 hydroxyethyl M.S.
The amount of cellulose ether (CMHEC) used in the practice of the
invention can vary widely depending upon the viscosity grade and
purity of the ether, and properties desired in the aqueous gels of
the invention. In general, the amount of cellulose ether (CMHEC)
used will be a water thickening amount, i.e., at least an amount
which will significantly thicken the water to which it is added.
Generally speaking, amounts in the range of about 0.5 to about 4
lbs/barrel, preferably from about 2 to 3 lbs/barrel of solution
will be used. However, amounts outside these ranges can be
used.
The term "increased viscosity" or the term "thickened" as used
herein in the descriptions with respect to the aqueous solutions,
is intended to mean any increase in the viscosity of a solution of
the polymer even up to the point where it is no longer flowable.
Thus, solutions can be prepared covering a wide range of
viscosities depending on the application intended.
As used herein, the term "brine" is intended to include any aqueous
solution of mineral salts having greater than 1,000 ppm solids
content, such as are frequently present in oil fields. Oil field
brines commonly contain varying amounts of sodium chloride, calcium
chloride, or magnesium salts. Also, flooding solutions are
frequently modified by the addition of potassium chloride to
stabilize the subsurface clay. Accordingly, potassium chloride is
also frequently encountered. In practical applications, such as the
post-primary petroleum recovery operations, the naturally occurring
brine which is encountered will be predominantly sodium chloride or
potassium chloride but a great number of other salts are almost
always present.
The aqueous medium in the present invention is preferably a hard
brine comprising on the order of 1,000 to 16,000 ppm divalent
cations such as preferably Ca++ with a total dissolved solids (TDS)
level in the range of 100,000 to 300,000 ppm. It is contemplated
that the inventive compositions would be most applicable in areas
characterized by the availability of highly saline field
waters.
The gelling agents, according to the invention, are the alkaline
earth metal (Group IIA) hydroxides, preferably calcium hydroxide.
The amount of gelling agent used in the practice of the invention
will be a small but finite amount which is effective or sufficient
to cause gelation when the alkaline earth metal hydroxide is mixed
with the remaining ingredients of the aqueous composition. In
general, the amount of gelling agent added will range from about
0.25 to about 4 lbs/barrel, preferably about 0.5 to about 3
lbs/barrel of solution.
Various methods can be used for preparing the aqueous gels of the
invention. The alkaline earth metal hydroxide can be first added to
a solution of CMHEC in the brine. Generally speaking, where
convenient, the preferred method is to first disperse the CMHEC in
the brine and then add the alkaline earth metal hydroxide to gel
the solution.
As water diversion agents and pusher fluids, respectively, the
inventive compositions can be injected at injection wells to
correct the permeability profile of a formation or for mobility
control in a post-primary oil recovery operation. The inventive
compositions can function as permeability correction agents by
temporarily decreasing water permeability in "thief zones" (high
permeability areas) and thus direct the subsequently injected drive
fluids to the less permeable, relatively oil-rich zones. The
effectiveness of such agents is reflected by the magnitude of the
increase observed in the oil-to-water ratio at surrounding
production wells. The instant compositions can function as pusher
fluids (mobility buffers), e.g., in surfactant flooding by
injecting the compositions as viscous slugs to push the previously
injected surfactant slug and recovered oil to a producing well. The
viscosity of the pusher fluid relative to that of the surfactant
slug, is such that little or no fingering of the slug into the
surfactant slug takes place.
As hydraulic fracturing fluids, the inventive compositions can be
employed to increase the production of oil from subterranean
formations. Hydraulic fracturing comprises the injection of a
suitable fracturing fluid down a well penetrating a formation and
into said formation under sufficient pressure to fracture the
formation. The resulting crack or fracture in the formation
provides a passageway which facilitates flow of fluids through the
formation and into the well. Propping agents can be included in the
inventive compositions if desired. Propping agents which can be
used include any of those known in the art, e.g., sand grains,
walnut shell fragments, tempered glass beads, aluminum pellets, and
similar materials, so long as they meet the appropriate
compatibility requirements. Generally speaking, it is desirable to
use propping agents having particle sizes in the range of 8 to 40
mesh (U.S. Sieve Series). However, particle sizes outside this
range can be employed. The observed gel strengths of the novel
composition (see Table I) indicate its superior proppant-carrying
ability.
It is contemplated that various known agents can be added to the
inventive compositions to minimize fluid loss to the formation
during fracturing operations. Apparently, these fluid loss
additives decrease the transfer of water into the formation by
temporarily plugging the exposed faces of the more accessible
channels and passages in the formation. One of the ways this is
done is by increasing the viscosity of the fracturing fluid. The
viscosity of the inventive fluid aids in minimizing this fluid
loss.
It is contemplated that the instant compositions have application
in the area of drilling muds, work-over fluids and completion
fluids. The suspending capacity of the fluids can be enhanced by
the presence of calcium ions under alkaline conditions which may be
effected by the addition of lime to the fluids containing CMHEC. A
mud with good suspending capacity can convey the large cuttings to
the surface where most of the cuttings can be removed. The mud
containing the cuttings must stand in a settling pit to allow the
cuttings sufficient time to settle out, or the cuttings can be
separated by cyclones or centrifuging.
The thickened compositions of the invention intended for use as
fracturing, water diversion or mobility buffer fluids can be
prepared on the surface in a suitable tank equipped with suitable
mixing means, and then pumped down the well and into the formation
employing conventional equipment for such compositions. However, it
is within the scope of the invention to prepare the compositions
while they are being pumped down the well. This technique is
sometimes referred to as "on the fly." For example, an aqueous
saline solution of the polymer can be prepared in a tank adjacent
the well head. Pumping of this solution through a conduit to the
well head can then be started. Then, a few feet downstream from the
tank, a suitable connection can be provided for introducing an
aqueous solution of an alkaline earth metal hydroxide such as
calcium hydroxide. As will be understood by those skilled in the
art, the rate of introduction of the components into the conduit
will depend upon the pumping rate of the inventive composition
through the conduit. Mixing orifices can be provided in the
conduit, if desired.
When prepared for use in drilling, completion and work over fluids,
the materials of this invention, can be prepared using conventional
mud mixing equipment. Polymer is generally added to the drilling
mud through jet hoppers discharging into the suction pit. Lime can
also be mixed through this jet hopper. The materials are in turn
mixed with the drilling mud by either jet or paddle mixers.
Hydration occurs as the mud is being mixed and pumped through the
bit nozzles.
It is within the scope of the invention to precede the injection of
the thickened composition as a fracturing fluid into the well and
out into the formation with a preflush of a suitable cooling fluid,
e.g., water. Such fluids serve to cool the well tubing and
formation and extend the useful operating temperature range of the
compositions. The volume of the cooling fluid so injected can be
any suitable volume sufficient to significantly decrease the
temperature of the formation being treated, and can vary depending
upon the characteristics of the formation. For example, amounts up
to 20,000 gallons, or more, can be used to obtain a temperature
decrease on the order of 100.degree. to 250.degree. F.
The following example further illustrates but should not be
considered as unduly limiting on the invention.
EXAMPLE I
A hard brine solution was prepared by mixing 3150 mL of saturated
sodium chloride solution (26 weight percent NaCl), 350 mL deionized
water and 150 g calcium chloride. Various amounts of
carboxymethylhydroxyethyl cellulose (CMHEC) were added to samples
of the hard brine and these mixtures were gelled by the addition of
hydrated lime. Apparent viscosities and gel strengths of the
thickened fluids were determined and the results are tabulated in
Table I.
TABLE I
__________________________________________________________________________
Apparent Viscosities and Gel Strengths of CMHEC/Hard Brine Mixtures
Gelled With Lime Concentration Gel Strengths, Run (lb/bbl).sup.a
Apparent Viscosities (cp) lbs/100 ft..sup.2 No. Run Type
CMHEC.sup.b Lime 51 Sec.sup.-1 102 Sec.sup.-1 170 Sec.sup.-1 340
Sec.sup.-1 511 Sec.sup.-1 1022 Sec.sup.-1 (10 sec/10
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min.) 1 Control 3 0 540 350 252 160.5 123 80.5 19/17 2 Invention 3
2 1550 1050 726 513 352 181.5 45/92 3 Control 4 0 1050 640 444 273
208 126.5 45/45 4 Invention 4 0.5 1660 1100 750 465 332 180 65/82
__________________________________________________________________________
.sup.a 1 g reagent per 350 mL solution is equivalent to 1 lb.
reagent per barrel of solution, e.g., 150 g CaCl.sub.2 in 3150 mL
saturated NaCl solution + 350 ml deionized water is equivalent to
15 lbs. CaCl.sub.2 per barrel of solution. .sup.b CMHEC420 was used
in these runs. CMHEC420 is carboxymethylhydroxyethyl cellulose with
a 0.4 degree of substitution and a 2 value for molar
substitution.
Referring to Table I, the greater gel strengths of the inventive
runs (No. 2 and No. 4) compared, respectively, to the control runs
(No. 1 and No. 3) indicate that the inventive thickened fluids
could advantageously be used to suspend cuttings in drilling muds
and proppants in fracturing fluids. The apparent viscosities show
that all the inventive and control fluids are thixotropic
(shear-thinning). A comparison of the apparent viscosities
exhibited by the inventive runs (No. 2 and No. 4) respectively,
with the control runs (No. 1 and No. 3) indicate that the lime
treatment greatly enhanced the apparent viscosity of the invention
runs. This suggests in particular that the inventive compositions
would be suitable for use as mobility buffers in carbonate
reservoirs.
* * * * *